It is well documented in the literature that unsaturated compounds containing a nucleophilic group and a reactive hydrogen atom in a position which favors ring closure may react with carbon monoxide to give cyclic (ring) derivatives. This invention concerns the synthesis of 5-membered ring lactams and their homologues through the metal catalyzed carbonylation of allylic substrates. The inventive process, as described therein, may be illustrated by the carbonylation reaction of equation (1) set forth below: ##STR1## wherein the desired product is a 5-membered ring lactam, the carbon valencies indicated are satisfied by hydrogen or alkyl, cycloalkyl, aryl, alkaryl or aralkyl groupings, each containing up to 12 carbon atoms, and X may be a halogen, chloride, bromide or iodide.
Alternatively, lactam synthesis may be effected from allylic amine substrates, as set forth in equation (2), wherein again the carbon valencies indicated are satisfied by hydrogen or alkyl, cycloalkyl, aryl, alkaryl or aralkyl groupings, each containing up to 12 carbon atoms. ##STR2##
The practice of this invention, as set forth in equation (1) and (2) is illustrated by:
(1) The preparation of .gamma.-butyrolactam from allylamine
(2) The synthesis of .gamma.-butyrolactam from allylic halides in the presence of carbon monoxide and ammonia.
(3) The synthesis of alkyl-substituted-.gamma.-butyrolactams from allylic halides in the presence of carbon monoxide and primary alkylamines.
The lactam products of this reaction are useful generally as organic intermediates. .gamma.-Butyrolactam, and its homologues, for example, may be important in the manufacture of polyamides, and as solvents for the separation of aromatic, aliphatic mixtures.
The preparation of lactams from allylic precursors using metal carbonyl or carbonyl precursors as catalysts in the literature*. Reviews by Falbe** and others summarize this work, particularly the synthesis of 5-membered ring lactams catalyzed by soluble cobalt catalysts. Unfortunately, many of these metal catalysts of the prior art have the intrinsic disadvantages of requiring stringent reaction conditions, particularly allylic isomerization and polymerization reactions. Furthermore they exhibit poor selectivity to the desired product and require the use of allylic amines as the allylic precursor (equation 2). FNT *J. Falbe and F. Korte, Chem. Ber. 98, 1928 (1965). FNT **"Carbon Monoxide in Organic Synthesis" by J. Falbe, Chapter IV, (1970).
This invention is directed to the use of certain homogeneous and heterogeneous rhodium catalysts which exhibit improved performances in the synthesis of 5-membered ring lactams, and their homologues, from allylic precursors. In practice this class of rhodium catalyst allows lactam synthesis under significantly milder conditions of temperature and pressure than has hitherto been possible with other metal carbonyl catalysts of the prior art, e.g. cobalt carbonyl catalysts. Furthermore, the rhodium catalysts of this invention allow the formation of lactams in higher yields, with improved selectivities to desired product and higher catalyst turnover numbers than has been practical in the prior art. A further demonstrated advantage of these rhodium catalysts is that used catalyst samples remain active after carbonylation of an allylic substrate is complete. Consequently, the used catalyst may be recycled with additional quantities of allylic substrate while demonstrating similar specific carbonylation activity to fresh catalyst material.
In the broadest practice of this invention, cyclic lactam products are produced from allylic precursors by the addition of carbon monoxide to an allylic material in the presence of a catalytic amount of rhodium catalyst, under elevated temperatures and pressures, in an oxygen-free environment, until the formation of the desired lactam products has taken place.
In the narrower practice of this invention, 5-membered ring lactams and their homologues, containing at least 4 carbon atoms, are produced by the catalytic reaction of carbon monoxide with an allylic halide by a process comprising the following steps:
(a) Admixing each mole of allylic halide to be carbonylated with at least a stoichiometric amount of an amine coreactant selected from the group consisting of ammonia or a primary amine, and at least a catalytic amount of homogeneous or heterogeneous rhodium catalyst, in the presence of a pressurized carbon monoxide atmosphere, to form a reaction mixture, and
(b) Heating said pressurized reaction mixture to 20.degree. C and above until substantial carbonylation of the allylic halide to the desired cyclic lactam derivative has taken place and isolating said desired .gamma.-lactam contained therein.
A further embodiment of the above described invention is the preparation of 5-membered ring lactams and their homologues containing at least 4 carbon atoms by a process comprising the following steps:
(a) Admixing each mole of allylic amine to be carbonylated with at least a catalytic quantity of a homogeneous or heterogeneous rhodium catalyst in the presence of a pressurized atmosphere of carbon monoxide, to form a reaction mixture, and
(b) Heating said pressurized reaction mixture to 20.degree. C and above until substantial carbonylation of the allylic halide to the desired cyclic lactam derivative has taken place and isolating said desired .gamma.-lactam contained therein.
In order to further aid in the understanding of this invention, the following additional disclosure is submitted: